1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display with improved optical efficiency.
2. Description of the Prior Art
As generally known in the art, a liquid crystal display (LCD) has been developed to replace a cathode ray tube (CRT) based on having merits in that it is lighter, thinner, shorter and smaller than CRT, in that it is driven at low voltage, and in that it consumes low electric power. Particularly, since a thin film transistor LCD (TFT LCD) has realized superior video quality, scale-up, coloring and so forth matchable for those of CRT, recently, it has been widely used in various areas as well as the notebook PC market and the monitor market.
Such LCDs, especially, TFT LCDs, comprise an array substrate having a TFT and a pixel electrode, and a color filter substrate coupled with the array substrate and having a color filter and a counter electrode, a liquid crystal layer being interposed between the array substrate and the color filter substrate. Further, orientation films for initial alignment of liquid crystal are mounted between the array substrate and the liquid crystal layer and between the color filter substrate and the liquid crystal layer. Still further, polarizers are attached to the outer sides of the respective substrates.
An LCD is a light-receiving display device which displays an image by means of light from an external source. Herein, a backlight is commonly used as an outer light source, which is mounted under the array substrate including the polarizers.
An LCD having a construction like the above displays certain picture image by operating liquid crystals of a pixel section between the array substrate and the color filter substrate with signaling through signal lines arranged in a matrix display.
Then, the LCD described above has a drawback in that the optical efficiency thereof is low. That is to say, LCDs have below 10% of substantially low optical efficiency because above 50% of optical loss occurs in the polarizer, partial optical loss also occurs in the color filters of red, green and blue, and the optical utilization rate is about 50% relative to the aperture ratio of pixels.
Herein, the aperture ratio in LCD is determined by the black-matrix formed on the color filter substrate. This black-matrix is formed so as to shut out light incident on a non-pixel section. Incident light on the black-matrix is completely absorbed into the black-matrix, so that the black-matrix causes optical loss.
FIG. 1 is a plan view of a color filter substrate, on which a black-matrix is formed, for explaining an LCD according to the prior art. FIG. 2 is a sectional view of an LCD according to the prior art.
Hereinafter, optical loss by the black-matrix and polarizer is now described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the color filter substrate comprises a pixel section, in which color filters 13a, 13b and 13c of red, green and blue are formed, and a non-pixel section that is a boundary between the pixel sections on which the black-matrix 12 is formed.
In the above construction, light incident on a region in which the color filters 13a, 13b and 13c of red, green and blue are formed is utilized so as to display picture image, but light incident on the other region on which the black-matrix 12 is formed is completely absorbed, thus causing optical loss.
As shown in FIG. 2, LCD comprises an array substrate 1 having a pixel electrode 2, a color filter substrate 11 coupled with the array substrate and having color filters 13a, 13b and 13c and the black-matrix 12, and a liquid crystal layer 20 interposed between the array substrate and the color filter substrate. Further, orientation films 4 and 14 for initial alignment of liquid crystal are mounted between the array substrate 1 and the liquid crystal layer 20 and between the color filter substrate 11 and the liquid crystal layer 20. Still further, polarizers 5 and 15 are attached to the outer sides of the respective substrates 1 and 11. Reference numeral 22 unexplained indicates a spacer inserted so as to maintain a distance between the substrates.
In an LCD constructed as above, light from a backlight (not shown in the drawings) is introduced to the inside a panel through a lower polarizer 5, wherein about 50% of optical loss occurs in course of polarization from unpolarized light to linearly polarized light.
Further, light traveling along an optical path A among the light incident inside the panel is utilized so as to display an image, but light traveling along an optical path B is completely absorbed in the black-matrix 12, so that the black-matrix causes optical loss.
In conclusion, in a conventional LCD as described above, the polarizer and the black-matrix cause considerable optical loss, so that the conventional LCD has very low optical efficiency.